The present invention relates to a process for production of water-soluble vegetable fibers from water-insoluble vegetable fibers which are residues obtained by defatting oil seeds such as soybeans and the like, and extracting protein therefrom (e.g., xe2x80x9cokaraxe2x80x9d and the like), or residues obtained by extracting starch from cereals. Further, the present invention relates to transparent biodegradable films, paste and chewing gum as well as low calorie food products using the water soluble vegetable fibers.
Residues obtained by extracting fats and oils from oil seeds and then extracting protein, or by extracting starch from, cereals are rich in vegetable fibers. However, it is difficult to recover the vegetable fibers in good yield because remaining protein entangles with vegetable fibers. Further, because of water-insolubility of these vegetable fibers, it is difficult to obtain water-soluble vegetable fibers in good yield with minimizing contamination of protein by degrading these water-insoluble vegetable fibers. For example, a residue, xe2x80x9cokaraxe2x80x9d, which is obtained by extracting fats and oils as well as protein from soybeans and the like are water-insoluble vegetable fibers still containing soybean protein. When the water-insoluble vegetable fibers are degraded with an alkali to extract water-soluble polysaccharides, the saccharides are degraded to oligosaccharides, or soybean protein, degraded soybean peptide and/or amino acids are contaminated. Thus, it is difficult to obtain highly purified vegetable fibers in a high yield.
At present, no process for recovering water-soluble vegetable fibers in high purity and high yield from such water-insoluble fibers has been found. If it were possible to obtain water-soluble vegetable fibers in high purity and high yield, such water-soluble vegetable fibers could be widely applied to various kinds of films and adhesives, food products and the like. For example, plastic package films are not naturally degraded. Although collagen films and pullulan films have biodegradable properties, i.e., capability for degradation by microorganisms, and the like, there are problems that collagen films have inferior heat-seal property, and pullulan films are expensive. On the other hand, it is possible to obtain the films without these problems by using the water-soluble vegetable fibers.
Further, adhesives such as animal glue, modified starch, gum arabic, pullulan, polyvinyl alcohol and the like, in particular, paste as remoistening adhesives have practical problems that their adhesive strength is low, they are expensive, and the like. However, such problems can be solved by using the water-soluble vegetable fibers.
Further, for example, when pullulan, which is water soluble polysaccharide produced by a microorganism, is used in chewing gum, pullulan is expensive in comparison with the water-soluble vegetable fibers, and the resulting chewing gum has inferior durability of pleasant chewing property and inferior water retention. However, when the water-soluble vegetable fibers is used, such problems can be solved.
Furthermore, the water-soluble vegetable fibers can be used for low calorie food products and such low calorie food products have not been known heretofore in the prior art.
The object of the present invention is to provide a process for production of water-soluble vegetable fibers from water-insoluble vegetable fibers containing protein, and is to provide films, paste, chewing gum and low calorie food products obtained by using the resulting water-soluble vegetable fibers.
The process for production of water-soluble vegetable fibers of the present invention comprises degrading water-insoluble vegetable fibers containing protein under acidic conditions of at about the isoelectric point of the protein and at a temperature of 130xc2x0 C. or lower.
As the water-insoluble vegetable fibers containing protein, there can be used residues obtained by removing husks, fats and oils and protein from oil seeds (e.g., soybeans, palm, coconut, corn, cottonseed, corn, etc.), and residues obtained by removing grounds, starch and the like from cereals (e.g., rice, wheat, etc.).
In the process of the present invention, it is suitable to degrade the water-insoluble vegetable fibers by heating at about an isoelectric point (normally, acidic range) of protein which is contained in the water insoluble vegetable fibers. Thereby, in comparison with alkaline degradation, contamination of protein in a degraded fraction can be minimized and no post step for removing protein is required to obtain water soluble-vegetable fibers having lower protein contents and high purity. Further, formation of any harmful material such as lysinoalanine or the like can be prevented and this is preferred from the viewpoint of productivity.
The pH about the isoelectric point of the protein contained in the water-insoluble vegetable fibers is normally within an acidic range (not higher than pH 6). For example, in the case of a residue obtained by extracting fats and oils and protein from soy beans, i.e. xe2x80x9cokaraxe2x80x9d, pH 3 to 6 is preferable.
Further, when husks such as peels and the like are contained in the water-insoluble vegetable fibers, the taste and flavor of the water-soluble vegetable fibers obtained becomes inferior and, therefore, in the present invention, it is preferred to use water-insoluble vegetable fibers from which husksxe2x80x94such as peels and the like are removed. When the water-insoluble vegetable fibers are obtained from oil seeds, green flavor and the like of the resulting water-soluble vegetable fibers can be reduced by using water-insoluble vegetable fibers from which husks and the like are removed. For example, in the case of xe2x80x9cokaraxe2x80x9d containing soybean protein, it is preferred to use xe2x80x9cokaraxe2x80x9d obtained from dehusked soybeans.
xe2x80x9cOkaraxe2x80x9d to be used in the present invention is a residue obtained by adding water to defatted soybeans from which its oil fraction has been extracted and removed, forming a slurry which contains okara and a water-soluble fraction by mixing the resultant mixture, e.g., with stirring and removing the water-soluble fraction, e.g., with centrifugation.
When the water-soluble fraction is subjected to isoelectric precipitation, e.g., by addition of an acid, it can be fractionated into soybean protein and whey. Whey contains carbohydrates containing oligosaccharides and proteins such as soybean albumin and the like.
xe2x80x9cOkaraxe2x80x9d contains water-insoluble fibers and soybean proteins which remain without extraction. Normally, xe2x80x9cokaraxe2x80x9d contains about 40 to 65% by weight of edible fibers based on the dry solids thereof. Suitably, xe2x80x9cokaraxe2x80x9d contains 10 to 40% by weight, preferably 10 to 20% by weight of proteins based on the dry solids thereof.
In the present invention, the reason why the water-insoluble vegetable fibers containing protein are degraded under acidic conditions at about the isoelectric point of protein is that the vegetable fibers are excessively degraded under considerably stronger acidic conditions than those at the isoelectric point of protein, for example, in the case of the degradation of xe2x80x9cokaraxe2x80x9d containing soybean protein as described above under strong acidic conditions of pH 2 or lower, which results in deterioration of functions as the vegetable fibers.. Further, protein is also degraded together with the vegetable fibers and dissolved and, thereby, when the fibers are used for drinks and the like, clouding of liquid is caused by neutralization. Furthermore, sufficient neutralization is required because of low pH and, therefore, the amount of a salt formed by neutralization increases, which requires an additional desalting step.
On the other hand, when water-insoluble vegetable fibers containing protein are degraded at a considerably higher pH than the isoelectric point of protein such as under neutral or alkaline conditions, for example, when xe2x80x9cokaraxe2x80x9dcontaining soybean protein as described above is degraded under alkali conditions, i.e., at a pH higher than 7, protein is degraded and dissolved together with the vegetable fibers and, therefore, clouding of liquid is caused, or browning tends to be caused by reaction of sugars with amino acids produced by degradation.
The reason why the water-insoluble vegetable fibers containing protein are degraded at a temperature of not higher than 130xc2x0 C. is that, when a temperature rises to higher than 130xc2x0 C., sugars produced by degradation (reducing sugars) react with amino acid to cause browning or an intense bad odor is caused. The temperature at which the water-insoluble vegetable fibers containing protein are degraded can be 130xc2x0 C. or lower. In order to carry out the degradation efficiently, the temperature should be higher than room temperature, preferably 80xc2x0 C. or higher, more preferably 100xc2x0 C. or higher.
Preferably, the water-soluble vegetable fibers produced by fractionating water-insoluble vegetable fibers at a high temperature under acidic conditions are further treated with activated charcoal to remove hydrophobic materials and low molecular weight materials and, thereby, the purity of the water-soluble vegetable fibers can be further improved.
The water-soluble vegetable fibers thus obtained contain water-soluble hemicellulose, for example, the water-soluble soybean fibers obtained from the residue of soybeans, xe2x80x9cokaraxe2x80x9d, are composed of rhamnose, fucose, arabinose, xylose, galactose, glucose and uronic acid as the constituent saccharide component, and have an average molecular weight of from 50,000 to 1,000,000, preferably from, 100,000 to 400,000.
In the present invention, the average molecular weight of saccharides is determined by measuring the viscosity in 0.1M sodium nitrate solution according to intrinsic viscosity using standard pullulan (manufactured by Hayashibara Seibutsu Kagaku Kenkyusho) as the standard substance. The proportion of saccharides are determined by the following analytical methods.
Uronic acid is determined by Blumen-Krantz method. Neutral saccharides are determined by alditol-acetate method.
The water-soluble vegetable fibers of the present invention thus obtained are superior in adhesive, film-forming properties, tensile properties of film, thickening properties (particularly, they have thickening properties within an alkaline range but, the viscosity is decreased under acidic conditions) and the like.
Hereinafter, transparent biodegradable films, paste, chewing gum and low calorie-food-prepared by using the water-soluble vegetable fibers of the present invention obtained from the water-insoluble vegetable fibers are illustrated.
The film of the present invention is a biodegradable film which has sufficient strength even in the form of a thin film, can be subjected to heat-sealing and is produced at a low production cost.
The biodegradable film can be prepared from the water-soluble vegetable fibers by using a known film forming method. For example, the water-soluble vegetable fibers can be extended on a plate or resin membrane in a suitable thickness and then they are dried to prepare the biodegradable film.
Further, in order to improve the properties of the biodegradable film, it is possible to add additives such as plasticizers, surfactants and the like. When such additives are used, it is preferred to select the additives so that they do not adversely affect the edibility of the above biodegradable film.
The paste of the present invention is an adhesive whose main component is the water-soluble vegetable fibers, particularly, the paste of the present invention is a remoistening adhesive.
When the protein content of the water-soluble vegetable fibers used is lower (normally, less than 10% by weight based on the dry solids), adhesion becomes stronger. Preferably, the protein content is not higher than 8% by weight, more preferably, not higher than 5% by weight.
The chewing gum of the present invention is that containing the water-soluble vegetable fibers.
In general, a chewing gum is composed of a gum base (normally, from 15 to 30% by weight), a sweetener (sugar, glucose, malt syrup and the like), and flavors and nutriments (normally, from 0.2 to 2% by weight). The gum base is composed of a natural resin, vinyl acetate resin, an ester gum, a synthetic gum, a natural wax, an emulsifying agent, calcium carbonate and the like.
Preferably, the content of the water-soluble vegetable fibers in the chewing gum of the present invention is from 1 to 40 parts by weight, preferably 2 to 30 parts by weight per 100 parts by weight of a gum base. In the case of a chewing gum such as flavored gum, bubble gum or the like, normally, the content of the water-soluble vegetable fibers of about from 0.2 to 10% by weight is preferred. In the case of a chewing gum containing less sweeteners, since as the content of saccharides is decreased, the amount of the water-soluble vegetable fibers is larger than this. When the content of the water-soluble vegetable fibers becomes too large, visco-elasticity is increased and the chewing gum becomes hard upon chewing. On the other hand, when the content becomes too small, the effect of the present invention is lost.
Since the dissolution rate in the mouth at a suitable content of the water-soluble vegetable fibers is slower than that of pullulan, superior durability of pleasant chewing properties and lasting of flavor can be obtained.
The low calorie food products of the present invention are food products composed of, as main raw materials, oils and fats and carbohydrate wherein a part of the raw materials is replaced with the water-soluble vegetable fibers to decrease the calories.